Elements, compounds and mixtures

Answer Key - Grade 10 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Ari splits 18 g of pure water into 2 g of hydrogen and 16 g of oxygen. How many grams of oxygen are in 63 g of pure water?

   56 g
2. 2.

   Esme splits 5 g of pure magnesium oxide into 3 g of magnesium and 2 g of oxygen. How many grams of oxygen are in 20 g of pure magnesium oxide?

   8 g
4. 3.

   Which box shows a pure compound, Jun?

   • Box A
   • Box D
   • Box C
5. 4.

   Which box has atoms of only one element but is still a mixture, Kira?

   Use the picture in question 3.

   • Box D
   • Box A
   • Box B
6. 5.

   Which box is a mixture of an element and a compound, Luz?

   Use the picture in question 3.

   • Box C
   • Box D
   • Box B

7. Read this first

   Boiling of four clear liquids at 1 atm (example data)

   sample	starts boiling (°C)	stops boiling (°C)
   P	78.4	78.4
   Q	78.4	91.0
   R	100.0	100.0
   S	100.6	104.0

8. 6.

   Which two samples look like pure substances, Milo?

   • P and R: each boils at one steady temperature
   • P and Q: each starts boiling at 78.4 °C and keeps going
   • R and S: each boils at nearly 100 °C, close to water
9. 7.

   Sample S is mostly water with something dissolved. Why does its boiling temperature climb, Noah?

   • The heater gets hotter as time passes, which lifts the boiling point of the liquid
   • Water leaves as vapor, so the solution gets stronger and boils hotter
   • Dissolved material turns into new water as the sample keeps boiling
10. 8.

    Ethanol boils at 78.4 °C. Sample Q boils from 78.4 to 91.0 °C. What does this suggest about Q, Pia?

    • It is pure ethanol, because boiling began at the temperature of ethanol
    • It is a compound that boils in two steps
    • It holds ethanol plus at least one liquid that boils higher

11. Three solids in a mix (real properties)

    solid	dissolves in water	attracted to a magnet
    iron filings	no	yes
    sand	no	no
    table salt	yes	no

12. 9.

    Sand, salt and iron filings are mixed dry. Which first step lifts one solid out without adding anything, Ren?

    • Filter the dry mixture through paper to catch the sand
    • Heat the mixture until the salt melts away from the others
    • Pass a magnet over it to lift out the iron filings
13. 10.

    The salt solution passed through the filter. How can the salt be recovered, Zee?

    • Filter it again, because salt is a solid in the water
    • Evaporate the water; the salt stays behind as crystals
    • Add more sand so the salt sticks to the sand