Answer: B) Ten moles of sodium hydroxide and five moles of hydrogen gas will be produced
Explanation: Got it right on USATestPrep
Answer:
We need 4.28 grams of sodium formate
Explanation:
<u>Step 1:</u> Data given
MW of sodium formate = 68.01 g/mol
Volume of 0.42 mol/L formic acid = 150 mL = 0.150 L
pH = 3.74
Ka = 0.00018
<u>Step 2:</u> Calculate [base)
3.74 = -log(0.00018) + log [base]/[acid]
0 = log [base]/[acid]
0 = log [base] / 0.42
10^0 = 1 = [base]/0.42 M
[base] = 0.42 M
<u>Step 3:</u> Calculate moles of sodium formate:
Moles sodium formate = molarity * volume
Moles of sodium formate = 0.42 M * 0.150 L = 0.063 moles
<u>Step 4:</u> Calculate mass of sodium formate:
Mass sodium formate = moles sodium formate * Molar mass sodium formate
Mass sodium formate = 0.063 mol * 68.01 g/mol
Mass sodium formate = 4.28 grams
We need 4.28 grams of sodium formate
It is 2.5g/ml. You can find this answer by taking the mass (25g) and dividing it by the volume (10ml) and you will get your answer of 2.5g/ml.
The half life of a substance is the time taken by a radioactive substance to decay by half its original mass. In this case, the half life of Potassium-40 is 1.3 billion years.
Original mass of Potassium-40 = 12 g (100%)
New mass after the decay = 3 g ( 25 %, since 75% was replaced by argon)
New mass = Original mass × (1/2)^n ; where n is the number of half lives.
3 = 12 × (1/2)^n
(1/2)^n = 1/4
n = 2
Therefore; the time taken will be 1.3 × 2 = 2.6 Billion years
