Important Chemistry Questions 2?

Question

1) Whats the halflife of an isotope if 12 grams of a 500 gram sample of the isotope if 125 grams of a 500 gram sample of the istope remains after 3 yrs?

a)1.5 years b)2.5 years C)3.5 Years d) 4.5 years


2) In the reaction represented by the equation Na+Br=NaBr, which species is reduced?

a)Na b)Br c)both a and b d) neither a or b

3) Predict the product of the reaction represented by MgO +CO2 =

a)MgCO3 b)Mg+ CO3 c) MgC+ O3 d)Mg(O2+o)


Thank you very much.

Answer 1

oxidation and reduction memory tool: OIL RIG

Oxidation
Is
Losing (electrons)

Reduction
Is
Gaining (electrons)

Answer 2

Half life doesn't change w/ the amount of product lost
125 is 1/4 of the original mass so divide the time by two and you have have the half life

Na+Br--->NaBr........NaBr----->Na(+) + Br(-)
so Na is losing electrons and Br is gaining them
oxidation is the loss of electrons
reduction is the gain of electrons

MgO + CO2 -----> MgCO3