HESI A2 Chemistry Test
25 Questions
Step-by-step Answer Explanations
Pass Guarantee
LATEST UPDATE
, 1. 1. Question
Which of the following is not a polysaccharide?
Starches
Glycogen
Cellulose
Glucose
Answer: Glucose
Polysaccharides are carbohydrates where more than one monosaccharide is bonded
together. Since glucose is only one molecule, it is a monosaccharide (also called a ‘simple
sugar’).
Examples of polysaccharides include starch and cellulose.
2. 2. Question
What percentage of an original sample of iodine-131 will remain after 64 days if iodine-131 has
a half-life of 8 days?
6.25%
25%
12.5%
0.39%
Answer: 0.39%
, First, determine the number of half-lives that will occur over a 64-day period. Do this by
dividing the 64-day period by the 8-day half-life.
64 ÷ 8 = 8
This tells us that there will be 8 half-lives during this 64 day period. The half-life of a substance
is the time is takes for that substance to decay. After each half-life, half of the starting amount
will have decayed. In this case, every 8 days, half of the amount of iodine-131 decays.
Since this problem doesn’t give us a starting amount and instead, asks us to find the percentage,
we can start by plugging in 100g as the starting amount. This way, the ending amount will
automatically give us the percentage that’s left, because it is already out of 100.
For each half-life, we divide the starting amount in half, like this:
Half-life: 1
100 → 50
Half-life: 2
50 → 25
Half-life: 3
25 → 12.5
Half-life: 4
12.5 → 6.25
Half-life: 5
6.25 → 3.125
Half-life: 6
3.125 → 1.5625
Half-life: 7
1.5625 → 0.78125
Half-life: 8
0.78125 → 0.390625
The ending amount is 0.39g out of 100g that we started with. Therefore, the remaining amount
after 8 half-lives (64 days) is 0.39% of the starting amount.
25 Questions
Step-by-step Answer Explanations
Pass Guarantee
LATEST UPDATE
, 1. 1. Question
Which of the following is not a polysaccharide?
Starches
Glycogen
Cellulose
Glucose
Answer: Glucose
Polysaccharides are carbohydrates where more than one monosaccharide is bonded
together. Since glucose is only one molecule, it is a monosaccharide (also called a ‘simple
sugar’).
Examples of polysaccharides include starch and cellulose.
2. 2. Question
What percentage of an original sample of iodine-131 will remain after 64 days if iodine-131 has
a half-life of 8 days?
6.25%
25%
12.5%
0.39%
Answer: 0.39%
, First, determine the number of half-lives that will occur over a 64-day period. Do this by
dividing the 64-day period by the 8-day half-life.
64 ÷ 8 = 8
This tells us that there will be 8 half-lives during this 64 day period. The half-life of a substance
is the time is takes for that substance to decay. After each half-life, half of the starting amount
will have decayed. In this case, every 8 days, half of the amount of iodine-131 decays.
Since this problem doesn’t give us a starting amount and instead, asks us to find the percentage,
we can start by plugging in 100g as the starting amount. This way, the ending amount will
automatically give us the percentage that’s left, because it is already out of 100.
For each half-life, we divide the starting amount in half, like this:
Half-life: 1
100 → 50
Half-life: 2
50 → 25
Half-life: 3
25 → 12.5
Half-life: 4
12.5 → 6.25
Half-life: 5
6.25 → 3.125
Half-life: 6
3.125 → 1.5625
Half-life: 7
1.5625 → 0.78125
Half-life: 8
0.78125 → 0.390625
The ending amount is 0.39g out of 100g that we started with. Therefore, the remaining amount
after 8 half-lives (64 days) is 0.39% of the starting amount.
