# Pure substances and mixtures Q&A KS3

```Pure substances and mixtures – Que &amp; Ans
Q1. Air is a mixture. Explain what does this means.
Air is a mixture because it consists of several gases that are able to be
separated by physical means. For example: oxygen, nitrogen etc. by physical
process.
Q2. Jofin claims that carbon dioxide is a mixture because it contains both
carbon and oxygen atoms. Is he correct? Explain why?
No carbon dioxide is not a mixture because carbon has chemically reacted with
oxygen. It is a compound because it has different chemical and physical
properties from the carbon and oxygen atoms which makes it.
Q3. Yasmin cooled down some water. It froze at -5 degree Celsius. What does
this tell her about the purity of water?
The freezing point of water is 0 degree Celsius but when Yasmin cooled it the
freezing temperature was -5 degree Celsius. So this indicates impurities are
present in water which lowered the freezing point of water. This means that
water is not pure.
Q4. 18 karat gold is 75% pure gold. An 18 karat gold ring has a mass of 4 g. How
much gold this contain?
75% of 4g =
75
100
&times; 4 = 3g
Q5. Evie uses a reaction to produce an insoluble substance and water. Describe
how she could separate the two products.
By filtration
```