krit.club logo

Chemical Substances - Separating Mixtures (Filtration, Distillation, Chromatography)

Grade 6IGCSE

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

🔑Concepts

•

A mixture consists of two or more substances that are physically combined but not chemically bonded, such as NaClNaCl (salt) mixed with H2OH_2O (water).

•

Filtration: A method used to separate an insoluble solid (like sand) from a liquid. The solid trapped in the filter paper is called the residue, and the liquid that passes through is the filtrate.

•

Evaporation: A process used to separate a soluble solid from a solvent by heating the solution until the liquid turns into a gas, leaving the solid crystals behind.

•

Simple Distillation: A technique used to separate a pure solvent from a solution. It involves boiling the solution to create vapor and then cooling the vapor in a condenser to turn it back into a liquid (H2O(g)→H2O(l)H_2O_{(g)} \rightarrow H_2O_{(l)}).

•

Paper Chromatography: A method used to separate different pigments or dyes in a mixture based on their solubility. The more soluble a substance is in the solvent, the further it travels up the paper.

•

States of Matter in Separation: These processes rely on physical properties such as solubility, particle size, and boiling points (e.g., H2OH_2O boils at 100∘C100^\circ C).

📐Formulae

Rf=Distance moved by the substanceDistance moved by the solvent frontR_f = \frac{\text{Distance moved by the substance}}{\text{Distance moved by the solvent front}}

Solvent+Solute=Solution\text{Solvent} + \text{Solute} = \text{Solution}

Rate of flow∝Solubility\text{Rate of flow} \propto \text{Solubility}

💡Examples

Problem 1:

A student has a mixture of sand and salt. Describe the steps required to obtain pure, dry sand and pure salt crystals.

Solution:

  1. Add H2OH_2O to the mixture and stir to dissolve the salt. 2. Filter the mixture to collect the sand as residue. 3. Wash the sand with a little distilled H2OH_2O and dry it. 4. Evaporate the filtrate (salt solution) to recover the NaClNaCl crystals.

Explanation:

Salt is soluble in H2OH_2O while sand is insoluble. Filtration separates the insoluble sand, and evaporation removes the solvent to leave the soluble salt.

Problem 2:

In a chromatography experiment, a red dye travels 4 cm4\text{ cm} from the baseline, while the solvent travels 10 cm10\text{ cm}. Calculate the RfR_f value.

Solution:

Rf=4 cm10 cm=0.4R_f = \frac{4\text{ cm}}{10\text{ cm}} = 0.4

Explanation:

The RfR_f value is a ratio used to identify substances; it is calculated by dividing the distance traveled by the component by the distance traveled by the solvent.

Problem 3:

Why is a condenser used in the distillation of H2OH_2O?

Solution:

The condenser cools the water vapor (H2O(g)H_2O_{(g)}) produced by boiling, causing it to undergo condensation back into liquid water (H2O(l)H_2O_{(l)}).

Explanation:

Distillation requires both evaporation (to separate the solvent from the solute) and condensation (to recover the solvent).