Chemistry Lab: Mixture Components Quiz

Questions and Answers

Suggest a way to determine whether a colorless liquid is pure water or a salt solution without tasting it.

Boil all the water away and if there is a residue, it is most likely a salt solution.

What distinguishes a mixture from an impure substance?

If a substance contained primarily one component, it's an impure substance; if it has similar amounts of several components, it's a mixture.

Define the process of sublimation.

When a solid passes directly into a gaseous state and back to a solid state without appearing in liquid state.

How do decantation and filtration differ, and which should be faster?

Decantation is when a liquid is poured away from a solid; filtration is when a liquid is poured through a filter and a solid is left afterwards. Decantation is faster. Signup and view all the answers

Why should you never place a hot object on the pan of a balance?

It creates a buoyancy effect and will appear to have a reduced mass. Signup and view all the answers

How did this experiment illustrate the principle of conservation of mass?

All of the original sample should be recovered; the sum of NH4Cl, SiO2, and NaCl should equal the total mass of the sample within experimental error. Signup and view all the answers

How could you separate zinc chloride from SiO2?

Zinc chloride is soluble, therefore it will be dissolved in the filtrate and the SiO2 will be a residue. Signup and view all the answers

Why is the NaCl extracted with water three times as opposed to only once?

You do it 3 times to get maximum extraction; you get 50% of the substance every time you extract. Signup and view all the answers

A student found that her mixture was 13% NH4Cl, 18% NaCl, and 75% SiO2. Assuming that her calculations are correct, what did she most likely do incorrectly in her experiment?

She didn't filtrate the mixture properly, not allowing substances to separate and dry during filtration. Signup and view all the answers

Study Notes

Determining Purity of a Liquid

To identify if a colorless liquid is pure water or a salt solution, boil the liquid; presence of residue indicates a salt solution.

Mixture vs. Impure Substance

An impure substance primarily contains one component, whereas a mixture has comparable amounts of multiple components.

Sublimation Process

Sublimation refers to the transition of a solid directly into a gas and back to solid without becoming liquid.

Decantation vs. Filtration

Decantation involves pouring off liquid from solids, while filtration passes liquid through a filter, leaving solids behind.
Decantation is generally faster since it doesn't require additional substances.

Balance and Hot Objects

Placing a hot object on a balance can create buoyancy effects, appearing to reduce the object's mass.

Conservation of Mass Principle

The conservation of mass is illustrated by recovering all original sample components, where the total mass of NH4Cl, SiO2, and NaCl equals the initial sample mass, within experimental error.

Separation of Zinc Chloride and SiO2

Zinc chloride is soluble and will dissolve in the filtrate during separation, leaving SiO2 as a residue.

Extraction Process of NaCl

NaCl is extracted with water three times to maximize extraction efficiency; each extraction provides approximately 50% recovery (e.g., first extraction: 50%, second: 75%).

Error in Mixture Composition

A student reporting a mixture composition of 13% NH4Cl, 18% NaCl, and 75% SiO2 likely failed to properly filter the mixture, affecting substance separation and drying.

Description

Test your knowledge on the separation of mixtures and the properties that distinguish mixtures from pure substances. This quiz covers methods to identify liquids and the definitions pertaining to mixtures and impurities. Perfect for chemistry lab students!