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.

   Bo splits 11 g of pure carbon dioxide into 3 g of carbon and 8 g of oxygen. How many grams of oxygen are in 33 g of pure carbon dioxide?

   24 g
3. 2.

   Which box shows a pure compound, Jun?

   • Box C
   • Box D
   • Box A
4. 3.

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

   Use the picture in question 2.

   • Box D
   • Box A
   • Box B
5. 4.

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

   Use the picture in question 2.

   • Box C
   • Box D
   • Box B

6. 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

7. 5.

   Which two samples look like pure substances, Milo?

   • R and S: each boils at nearly 100 °C, close to water
   • P and R: each boils at one steady temperature
   • P and Q: each starts boiling at 78.4 °C and keeps going
8. 6.

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

   • Dissolved material turns into new water as the sample keeps boiling
   • Water leaves as vapor, so the solution gets stronger and boils hotter
   • The heater gets hotter as time passes, which lifts the boiling point of the liquid
9. 7.

   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

10. 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

11. 8.

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

    • Heat the mixture until the salt melts away from the others
    • Filter the dry mixture through paper to catch the sand
    • Pass a magnet over it to lift out the iron filings
12. 9.

    The iron is out. Sand and salt are stirred into water and poured through filter paper. What stays on the paper, Tala?

    • Nothing: both solids dissolve in water
    • The sand: salt dissolves into tiny ions that pass through with the water
    • Both solids: the salt crystals are too big to pass through the paper
13. 10.

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

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