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Materials and Matter - Mixing and Separating Substances

Grade 4IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Matter is everything around us and typically exists in three states: solids, liquids, and gases. Water, represented as H2OH_2O, can exist in all three states depending on temperature.

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A mixture is formed when two or more substances are combined physically but not chemically. The substances in a mixture keep their own properties.

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A solution is a special type of mixture where one substance (the solute) dissolves completely into another (the solvent). For example, mixing salt (NaClNaCl) into water (H2OH_2O).

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Solubility refers to the ability of a substance to dissolve. Factors like stirring and increasing the temperature (TT) of the solvent usually increase the rate at which a solute dissolves.

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Sieving is a method used to separate mixtures of different sized solids, such as separating stones from sand.

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Filtration is used to separate an insoluble solid (like sand) from a liquid (like H2OH_2O). The solid trapped is called the residue, and the liquid passed through is the filtrate.

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Evaporation is used to recover a dissolved solute (like sugar) from a solvent. The liquid is turned into gas, leaving the solid behind.

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Magnetism can be used to separate magnetic metals like Iron (FeFe) or Nickel (NiNi) from non-magnetic substances.

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Decanting is a simple method of separating a heavier insoluble solid from a liquid by carefully pouring the liquid off the top.

📐Formulae

Solution=Solute+SolventSolution = Solute + Solvent

Concentration=Mass of SoluteVolume of SolventConcentration = \frac{Mass\ of\ Solute}{Volume\ of\ Solvent}

H2O(s)→heatH2O(l)→heatH2O(g)H_2O_{(s)} \xrightarrow{heat} H_2O_{(l)} \xrightarrow{heat} H_2O_{(g)}

💡Examples

Problem 1:

How would you separate a mixture containing sand, salt (NaClNaCl), and iron filings (FeFe)?

Solution:

  1. Use a magnet to extract the FeFe filings. 2. Add H2OH_2O to the remaining sand and salt to dissolve the NaClNaCl. 3. Use filtration to separate the sand from the saltwater. 4. Use evaporation to remove the H2OH_2O and leave the NaClNaCl crystals.

Explanation:

This uses the physical properties of magnetism, solubility, and boiling points to isolate each substance.

Problem 2:

If you have 20 g20\ g of salt dissolved in 200 mL200\ mL of water, and you add another 200 mL200\ mL of water, what happens to the concentration?

Solution:

The concentration decreases.

Explanation:

The mass of the solute remains 20 g20\ g, but the volume of the solvent increases from 200 mL200\ mL to 400 mL400\ mL. Using the formula C=mVC = \frac{m}{V}, the concentration becomes 20 g400 mL=0.05 g/mL\frac{20\ g}{400\ mL} = 0.05\ g/mL instead of the original 0.1 g/mL0.1\ g/mL.

Problem 3:

Why does sugar dissolve faster in tea at 80∘C80^\circ C than in iced tea at 5∘C5^\circ C?

Solution:

Higher temperature (TT) increases the kinetic energy of the molecules.

Explanation:

At 80∘C80^\circ C, the H2OH_2O molecules move faster and collide with the sugar crystals more often, breaking them down into the solution more quickly than at 5∘C5^\circ C.

Mixing and Separating Substances - Revision Notes & Key Formulas | IB Grade 4 Science