m2 chemistry review for midterm

Sort the substances into their appropriate groups.

Groups:

(a) Homogeneous mixture

,

(b) Heterogeneous mixture

,

(c) Pure compound

,

(d) Pure element

• water

• sugar and water

• sugar and oil

• gold

• sand and water

• oxygen

• carbon dioxide

• saline

Answer explanation

Homogenous mixtures are completely uniform (the same throughout), the particles are tiny and they cannot be filtered. Eg. saline is the same saltiness throughout.

Heterogenous mixtures are not uniform. For example sugar in oil, the bottom is sugary and the top is oily. Usually the parts can be seen with the naked eye.

Compounds contain particles each of which is composed of more than one element from the period table. eg. particles of carbon and oxygen react together to form a new particle called carbon dioxide. Carbon dioxide is chemically different and has a new set of properties, but it is still a pure substance.

Elements are composed of atoms which are all more or less identical (crucially the proton number).

10 g of sugar is added to 100 g of water to make 110g of syrup. Match the correct mixture terminology to each substance.

• solution

• water

• solvent

• sugar

• solute

• syrup

Answer explanation

The solute dissolves into the solvent to form a solution. The solute tends to be the smaller part, and takes on the state of the solvent... eg sugar, a solid, becomes like water, a liquid.

The image shows a heterogeneous mixture of sand and salt. Arrange the processes in the correct order to separate and extract the salt.

• shake well

• evaporate the water

• add water

• filter the mixture

Answer explanation

This would be a difficult mixture to physically separate. However, we know that salt dissolves in water, whereas sand is totally insoluble in water.

Therefore: add water then mix

then filter, then evaporate the water to isolate the salt

The diagram illustrates the filtration of mixtures, including sand, saline solution, and syrup. Classify the feed substances into those that primarily remain in the residue or pass into the filtrate.

Groups:

(a) Residue

,

(b) Filtrate

• sugar

• sand

• water

• salt

Answer explanation

feed is a mixture that goes into a filter

the residue gets trapped in the filter

the filtrate goes straight through the filter.

In a glass of lemonade made by dissolving sugar in water and adding a few drops of lemon juice, which of the following is the solute, solvent, and solution?

• 1. Solute: Sugar,

  2. Solvent: Water,

  3. Solution: Lemonade

• 1. Solute: Water,

  2. Solvent: Lemonade,

  3. Solution: Sugar

• 1. Solute: Lemon juice,

  2. Solvent: Sugar,

  3. Solution: Water

• 1. Solute: Lemonade,

  2. Solvent: Water,

  3. Solution: Sugar

Answer explanation

The solute dissolves into the solvent to form a solution. The solute tends to be the smaller part, and takes on the state of the solvent... eg sugar, a solid, becomes like water, a liquid.

500 ml of syrup is discovered to contain 50 g of sucrose (table sugar).

Which concentration accurately represents this?

• 10% m/v

• 10% v/m

• 9% m/v

• 9% v/m

Answer explanation

the solute mass of 50 g is already a component of the solution with volume 500 ml

hence (50/500) x 100 10% m/v

A simple distillation separates substances based on their...

• solubility

• particle size

• boiling point

• density

Answer explanation

Distillation takes advantage of differing boiling points.

A common use is the desalination of seawater to isolate pure drinking water. Water boils at the relatively low temperature of ca. 100°C whereas salt boils at whopping 1413°C!!!!

The diagram shows a simple distillation setup being used to separate a mixture of water and ethanol. Ethanol has a boiling point of 78°C. If the thermometer reads 90°C during the process, what substances are collected as liquids X and Y?

• X is water and Y is ethanol

• X is ethanol and Y is water

• X is water and ethanol and Y is ethanol

• X is ethanol and Y is water and ethanol

The diagrams illustrate the steps involved in paper chromatography. Arrange them in the correct chronological order.

• 
• 
• 
• 

Calculate the Rf value for the yellow component to the nearest 0.1

• 0.5

• 0.6

• 0.8

• 0.9