Ar and Mr

Question 1

How is the Mr calculated

Answer 1

1. Find out how many atoms of each element there are
2. Adding the Ar values together

Question 2

Figure out the Mr of Ca(OH) 2

Ca=40
O=16
H=1

Answer 2

Mr = 40 (ca) + 2x16 (O x 2) + 2x1 (H x 2) = ?

40+32+2 = 72

Question 3

What is the law of conservation of mass

Answer 3

No atoms are lost or made in a reaction

Question 4

48g of magnesium and an unknown number of oxygen creates 80g of magnesium oxide, how much oxygen is needed?

Answer 4

80-48 = ?
32g of oxygen

Question 5

Explain the reactions that occur in a closed system

Answer 5

The reactants and products stay in the same beaker, so the mass of the beaker and substances stay the same

Question 6

Explain the reactions in a non-closed system

Answer 6

Substances can leave or enter the system, if the gas escapes then the total mass looks as if it decreased and vice versa, however the total mass stays the same if the mass of gas in included.

Question 7

Explain the change of mass in:
CaCO3 -> CaO(s) + CO2(g)
10g 5.6g

Answer 7

The total mass appears to have decreased as carbon dioxide has escaped to the air. The total mass is still 10g