C1.3 Purity and Separating Mixtures

Question 1

Pure Substance

Answer 1

A substance only made of one type of element or compound

Question 2

Mixture

Answer 2

A combination of different elements and/or compounds that are not chemically bonded

Question 3

Alloy

Answer 3

A mixture of two or more metals. It is a type of formulation

Question 4

Formulation

Answer 4

Useful mixtures with a specific purpose that have an exact ratio that is a measured quantity

Question 5

Exam-Style Question

A student has a sample of liquid that he thinks is citric acid. Citric acid (C₆H₈O₇) has a boiling point of 310°C. The students heats the sample and it has a boiling point of 335°C. Is the sample pure citric acid? Explain why.

(2 marks)

Answer 5

no (1)
because
the boiling point is higher than citric acid (impurities increase the boiling point of the sample) (1)
do not give any marks for yes

Question 6

What would be the difference between the melting point of a pure substance and a sample containing the compound and other impurities?

Answer 6

It would be lower

Question 7

When a scientist heats a block of metal a part of the mixture melts before the rest. What does this tell us about the block of metal?

Answer 7

It is impure

Question 8

Simple Distilation

Answer 8

Separates a liquid from a solution