Atoms and Molecules

Joseph Proust experimented with which compounds to establish the Law of Constant Proportions?

Dalton suggested that the smallest unit of matter is the _____.

In the reaction between Sodium Carbonate and Ethanoic Acid, if the total mass before reaction is $11.3$ g, the total mass after reaction (including residue and gases) will be:

Pure water can be obtained from a well, a river, or even synthesized in a lab. In all cases, the ratio of $H:O$ by mass is $1:8$. This proves:

In a laboratory setup, a scientist introduces $28\,g$ of Nitrogen gas and $10\,g$ of Hydrogen gas into a sealed reaction vessel. They react to form Ammonia ($NH_3$), where Nitrogen and Hydrogen always combine in a fixed mass ratio of $14:3$. According to the Laws of Chemical Combination, what is the total mass of the substances (including products and any unreacted reactants) inside the vessel after the reaction is complete?

Two elements, $X$ and $Y$, react to form a specific compound. The provided diagram shows the data from two separate experiments conducted to synthesize this compound. Based on the Law of Constant Proportions, what is the value of '$M$' (the mass of element $Y$) in Experiment 2?

What mass of silver nitrate will react with $5.85\,g$ of sodium chloride to produce $14.35\,g$ of silver chloride and $8.5\,g$ of sodium nitrate?

The ratio of the masses of $H$ and $O$ in $H_2O$ is $1:8$, and in $H_2O_2$ it is $1:16$. This demonstrates that for a fixed mass of hydrogen ($1\text{ g}$), the masses of oxygen ($8\text{ g}$ and $16\text{ g}$) are in the ratio $1:2$. This is an example of:

Dalton's postulate that 'Atoms can neither be subdivided, created nor destroyed' is essentially a restatement of:

In the reaction $S + O_2 \rightarrow SO_2$, $32\text{ g}$ of Sulphur reacts with $32\text{ g}$ of Oxygen to form $64\text{ g}$ of Sulphur Dioxide. What mass of $SO_2$ is formed if $32\text{ g}$ of Sulphur is reacted with $48\text{ g}$ of Oxygen?

The relative atomic mass of Carbon-12 is exactly:

Who was the scientist that proposed each element has a characteristic atomic mass?

Which element has an atomic mass that is almost exactly double its atomic number ($14$)?

If the atomic mass of Hydrogen is 1 and Oxygen is 16, what is the molecular mass of water ($H_2O$)?

Using the data provided in the flowchart regarding the composition and atomic masses of Magnesium and Chlorine, calculate the total formula unit mass of Magnesium Chloride ($MgCl_2$).

Which of these pairs has approximately the same atomic mass?

If an element $X$ has an atomic mass of $31 u$, it is most likely:

If $N_{A}$ atoms of an element weigh $M$ grams, what is the mass of a single atom of that element in atomic mass units?

What is the relative formula mass of Ammonium Phosphate $(NH_{4})_{3}PO_{4}$? ($N=14, H=1, P=31, O=16$)

In the molecule $C_{12}H_{22}O_{11}$, the ratio of the mass of Carbon to the mass of Hydrogen is:

The ratio by mass of Nitrogen to Hydrogen in Ammonia ($NH_3$) is:

What is the symbol for the Silver ion?

Which of the following is a neutral molecule?

The valency of Aluminum is:

A molecule of Ammonium Sulphate is formed by the combination of ions as shown in the diagram. Calculate the molecular mass of one molecule of Ammonium Sulphate. (Given atomic masses: $N = 14 \text{ u}, H = 1 \text{ u}, S = 32 \text{ u}, O = 16 \text{ u}$)

An element $X$ reacts to form a specific cation as shown in the process below. If this cation combines with the polyatomic phosphate ion ($PO_4^{3-}$), what would be the correct chemical formula for the resulting ionic compound?

A student analyzes two different samples of water ($H_2O$) as illustrated in the diagram. If Sample 1 contains $20 \text{ g}$ of Hydrogen for every $160 \text{ g}$ of Oxygen, what mass of Oxygen would be present in Sample 2 if it is found to contain $5 \text{ g}$ of Hydrogen, following the Law of Constant Proportions?

Which of the following ions is a polyatomic ion?

Calculate the number of molecules of phosphorus ($P_4$) present in 31 g of phosphorus. (Atomic mass of $P = 31$)

How many moles of magnesium phosphate, $Mg_3(PO_4)_2$ will contain 0.25 mole of oxygen atoms?

What is the name of the compound with the formula $NH_4Cl$?

The formula for Sodium Oxide is:

What is the chemical symbol for Tin?

What is the valency of Calcium?

What is the formula for Iron (II) Hydroxide?

The formula for Magnesium Nitrite is:

What is the chemical formula for Phosphorus Pentachloride?

Which of the following correctly describes the 'Law of Constant Proportions' in the context of writing a chemical formula?

If a metal $M$ forms a compound $M_2S_3$, the formula of its chloride is:

The mass ratio of hydrogen to oxygen in hydrogen peroxide ($H_2O_2$) is:

Which of the following has the maximum number of atoms?

Molar mass is the mass of ____ of a substance.

The chemical formula of Calcium Hydroxide is:

What is the mass of 2 moles of Hydrogen atoms (H)?

The diagram below represents the thermal decomposition of Calcium Carbonate ($CaCO_3$). Based on the Law of Conservation of Mass and the mole concept, calculate the number of moles of $CO_2$ gas produced. (Atomic masses: $Ca = 40, C = 12, O = 16$)

A student compares two different samples of oxygen as shown in the flowchart below. If $X$ represents the number of molecules in Sample 1 and $Y$ represents the total number of atoms in Sample 2, which mathematical relationship correctly links $X$ and $Y$?

Which of the following is a diatomic molecule?

The total number of protons in $10\text{ g}$ of Calcium Carbonate ($CaCO_3$) is: (Atomic numbers: $Ca=20, C=6, O=8$)

What is the mass of $1.5\text{ moles}$ of $Ca(OH)_2$? (Atomic masses: $Ca=40, O=16, H=1$)

An element $A$ is tetravalent and $B$ is divalent. The formula of the compound formed by these elements is:

If $12\ g$ of Magnesium burns in Oxygen to produce $20\ g$ of Magnesium Oxide, the mass of Oxygen used is:

Which postulate of Dalton's theory explains the Law of Constant Proportions?

In Ammonia ($NH_3$), if we have $17\ g$ of the compound, what is the mass of Nitrogen present, given the ratio is $14:3$?

When $4.0\ g$ of Hydrogen is reacted with excess Oxygen, $36.0\ g$ of water is formed. What mass of Oxygen was consumed?

Dalton's atomic theory suggested that atoms of the same element are identical in mass. We now know this is not always true because of:

Which of the following pairs of substances can be used to prove the Law of Constant Proportions?

A sample of $CaCO_3$ contains $40\%$ Calcium, $12\%$ Carbon, and $48\%$ Oxygen by mass. If you have $250\ g$ of $CaCO_3$, what is the mass of Calcium in it?

A student accidentally leaves the lid off a crucible while heating magnesium. The mass of the product is found to be greater than the mass of the starting magnesium. This observation:

Two elements P and Q combine to form a compound. If $1.0\ g$ of P reacts with $4.0\ g$ of Q, what is the percentage by mass of element P in the compound?

If $12\ g$ of carbon is burnt in $32\ g$ of oxygen, $44\ g$ of $CO_2$ is produced. If $12\ g$ of carbon is burnt in $50\ g$ of oxygen, $44\ g$ of $CO_2$ is still produced. Which law explains why $6\ g$ of oxygen is not simply 'added' to the $CO_2$?

Which of the following elements exists as a monoatomic molecule?

The valency of the Nitride ion is:

The molecular mass of $CO_{2}$ is: (Atomic mass: $C=12u, O=16u$)

The symbol for the Ferrous ion (Iron II) is:

The Law of Constant Proportions states that in a chemical substance, the elements are always present in definite proportions by mass. Based on the experimental data provided in the diagram for a compound formed by elements X and Y, what mass of element X is required to react completely with 32 g of element Y?

A specific ion 'X' is classified according to the properties shown in the flowchart below. Which of the following chemical species could represent the 'Target Ion'?

The chemical formula of Sodium Hydroxide is:

The percentage by mass of nitrogen in urea, $NH_{2}CONH_{2}$, is approximately:

Calculate the number of molecules in $1\ mg$ of Hydrogen gas ($H_{2}$).

The ratio of Carbon to Oxygen by mass in $CO$ is $3:4$. In $CO_{2}$, the ratio of Carbon to Oxygen by mass is $3:8$. This observation is a direct consequence of which of Dalton's postulates?

Which of the following elements has the lowest atomic mass?

Which of these elements has the highest atomic mass?

An atom with 2 protons and 2 neutrons has an atomic mass of:

An atom with 1 proton and 0 neutrons has an atomic mass of:

What is the chemical formula for Aluminium Sulphide?

The formula for Carbonic Acid (Hydrogen Carbonate) is:

Identify the formula for Ammonium Sulphate.

The ratio by mass of Hydrogen to Oxygen in water is $1:8$. If we take $3\ g$ of Hydrogen, what mass of Oxygen is required to react completely, and what will be the mass of water formed?

If the atomic mass of Calcium is $40\ u$, how many Calcium atoms are there in $2\ u$ of Calcium?

A sample of pure Magnesium contains $79\%$ of $Mg-24$, $10\%$ of $Mg-25$, and $11\%$ of $Mg-26$. Calculate the average atomic mass.

If $5.3\ g$ of sodium carbonate reacts with $6.0\ g$ of ethanoic acid, and $2.2\ g$ of carbon dioxide is released, what is the mass of the remaining solution?

The Law of Conservation of Mass is also known as the Law of Indestructibility of ________.

Conservation of mass is a fundamental principle in which branch of science?

If $12\ g$ of carbon is burnt in the presence of $32\ g$ of oxygen, how much $CO_2$ will be formed?

In the reaction $H_2 + Cl_2 \rightarrow 2HCl$, if $2 \text{ g}$ of hydrogen reacts with $71 \text{ g}$ of chlorine, the mass of hydrogen chloride produced is:

What happens to the total number of atoms during a chemical reaction according to the Law of Conservation of Mass?

During a chemical reaction, if $10 \text{ g}$ of A reacts with $20 \text{ g}$ of B and $5 \text{ g}$ of A is left unreacted, what is the total mass of the products and the unreacted reactant?

In a reaction where $A + B \rightarrow C$, if the mass of $A$ is $x$ and the mass of $B$ is $y$, the mass of $C$ must be $x+y$ according to the Law of Conservation of Mass. If $x=5.5g$ and $y=2.5g$, but only $7.8g$ of $C$ is recovered, what is the most likely explanation in a high-precision lab?

In a reaction between lead nitrate and potassium iodide, the mass of the beaker and the reactants is $25.35g$. After the reaction, a yellow precipitate is formed. What will be the mass of the beaker and its contents?

If $10.0g$ of $A$ reacts with $5.0g$ of $B$ to form $12.0g$ of $C$, and some unreacted $B$ remains, how much $B$ was left?

The ratio $14:3$ for Ammonia is a ratio of ________.

A chemical compound is always found to be made up of the same ________ combined together in the same fixed proportion by mass.

Two different samples of the same compound are found to have the same percentage of elements. This confirms which law?

The Law of Constant Proportions applies to ________.

In Phosphorus Pentoxide ($P_2O_5$), the mass ratio of $P:O$ is $31:40$. How much Phosphorus is in $71 \text{ g}$ of the compound?

If $10 \text{ g}$ of element A reacts with $20 \text{ g}$ of element B to form compound AB, what is the mass ratio $A:B$?

Which of these is a mathematical expression of the Law of Constant Proportions for a compound $A_xB_y$?

If a sample of methane ($CH_{4}$) is taken from a natural gas well and another is synthesized in a lab, which property will be identical according to Proust's Law?

In Potassium Chlorate ($KClO_{3}$), the mass ratio of $K:Cl:O$ is $39:35.5:48$. What is the percentage of Chlorine in the compound?

If the Law of Constant Proportions is followed, what happens to the mass ratio of elements in a compound if the total mass of the compound is doubled?

Which part of Dalton's theory was proven wrong later?

What remains constant in a given compound according to Dalton?

Dalton's atomic theory provided a scientific definition for:

All elements, compounds, and mixtures are composed of:

According to Dalton, why can we not change one element into another by a chemical reaction?

In the reaction $2H_2 + O_2 \rightarrow 2H_2O$, Dalton's theory suggests the total number of atoms of Hydrogen on the reactant side is:

When Dalton said 'atoms are indivisible', he meant they were:

Which of the following is the most scientifically accurate reason why Dalton's Atomic Theory is still taught despite its flaws?

Dalton's theory did not account for which of the following?

A sample of pure Calcium Carbonate ($CaCO_3$) always contains $40\%$ Calcium, $12\%$ Carbon, and $48\%$ Oxygen by mass. This is a direct application of Dalton's postulate regarding:

The term 'mole' was introduced by:

Who was the first scientist to use the symbols for elements in a specific sense?

The mass of 0.5 moles of water molecules is:

Which of the following is the correct symbol for Lead?

In Methane ($CH_4$), the elements Carbon and Hydrogen are always present in a fixed ratio of $3:1$ by mass. If a purified sample of methane is analyzed and found to contain exactly $12$ g of Hydrogen, what is the total mass of the methane sample?

A student is using the 'criss-cross' method to determine the formula of a compound. If element 'M' is a metal with a valency of 2 and element 'X' is a non-metal with a valency of 3, identify the correct chemical formula as indicated by the logic in the diagram.

The diagram below illustrates the process of electron transfer during the formation of an ionic compound between Magnesium and Chlorine. Based on this transfer, what is the net charge on the Magnesium ion in the final compound?

Which of the following postulates of Dalton's atomic theory explains the Law of Constant Proportions?

A sample of Magnesium Carbonate ($MgCO_3$) contains $2.4\text{ g}$ of Magnesium. What is the mass of Carbon in the sample?

How many moles are present in $342\text{ g}$ of Cane Sugar ($C_{12}H_{22}O_{11}$)?

The atom that loses an electron in the formation of an ionic bond is typically a:

Which of the following statements is correct about covalent compounds?

In the compound $MgO$, Magnesium __________ electrons to Oxygen.

Which type of bond is present in a molecule of $HCl$ gas?

The directionality of bonds is a characteristic of:

Covalent compounds are generally insoluble in water but soluble in organic solvents. Which of the following is an exception (soluble in water)?

If an atom of element X has a configuration 2, 8, 2 and Y has 2, 8, 7, what is the formula of the compound formed between them?

An unknown solid substance $S$ is subjected to a series of experimental tests as shown in the flowchart below. Based on these observations, which of the following statements correctly identifies the nature of substance $S$ and provides the scientific reasoning?

When comparing the lattice energy of $LiCl$ and $NaCl$, which one is expected to be higher and why?

Silicon dioxide ($SiO_2$) has a very high melting point. This is because:

Which of these molecules has the highest molecular mass?

What is the molecular mass of Phosphorus pentachloride ($PCl_{5}$)? (Atomic mass: $P = 31 u, Cl = 35.5 u$)

Calculate the molecular mass of Butane ($C_{4}H_{10}$). (Atomic mass: $C = 12 u, H = 1 u$)

The relative molecular mass of a molecule is compared to which standard?

Calculate the molecular mass of Butane ($C_4H_{10}$). (Atomic masses: $C = 12\ u, H = 1\ u$)

What is the molecular mass of Phosphorus pentachloride ($PCl_5$)? (Atomic masses: $P = 31\ u, Cl = 35.5\ u$)

Calculate the molecular mass of Hydrogen bromide ($HBr$). (Atomic masses: $H = 1\ u, Br = 80\ u$)