Why things dissolve: polarity, electrolytes and nonelectrolytes

Answer Key - Grade 10 Science Worksheet - Building Confidence

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

1. 1.

   Each unit of table salt (NaCl) splits into 2 ions in water. How many moles of ions come from 0.5 mol of salt, Ari?

   1 mol
2. 2.

   Each unit of baking soda (NaHCO₃) splits into 2 ions, Na⁺ and HCO₃⁻. How many moles of ions come from 0.25 mol, Kira?

   0.5 mol
3. 3.

   Why does salt dissolve in water but not in cooking oil, Jun?

   • Water is polar, like salt's charged ions; oil is not
   • Oil is too thick and oily for salt crystals to sink into it
   • Salt melts in water but not in oil
4. 4.

   Why don't oil and water mix, Luz?

   • Oil melts and floats away
   • Oil dissolves in water once it is stirred long enough
   • Water is polar and oil is nonpolar
5. 5.

   Which dissolves best in water, Milo?

   • Sugar
   • Candle wax
   • Cooking oil, once it is warmed
6. 6.

   Is sugar water an electrolyte, Pia?

   • Yes: sugar splits into charged ions in water
   • Yes, if enough sugar is added
   • No: sugar stays as whole molecules
7. 7.

   Which of these is an electrolyte in water, Ren?

   • Pure distilled water by itself
   • Baking soda, which forms Na⁺ and HCO₃⁻
   • Sugar, which forms sugar ions
8. 8.

   In a water molecule, which end is slightly negative, Tala?

   • Neither: water has no charged ends
   • The hydrogen end
   • The oxygen end
9. 9.

   Which end of water molecules faces an Na⁺ ion, Zee?

   • The positive hydrogen end
   • Both ends equally, at random
   • The negative oxygen end
10. 10.

    Which end of water molecules faces a Cl⁻ ion, Esme?

    • The negative oxygen end
    • Neither end: Cl⁻ stays in its crystal
    • The positive hydrogen end