For this question, assume that you have 1 compound. This compound is divided in half once, so you are left with 0.5. That 0.5 that remains is divided in half again, this is the second half-life, and you are left with 0.25. The final half life involves dividing 0.25 in half, which means you are left with 0.125. For the answer to make sense, you need to know your conversions between decimals and fractions. To make it simple, if you have 0.125 and you times it by 8, you are left with your initial value of 1. Therefore, after three half-lives, you are left with 1/8th of the compound.
Answer:
Approximately 75%.
Explanation:
Look up the relative atomic mass of Ca on a modern periodic table:
There are one mole of Ca atoms in each mole of CaCO₃ formula unit.
- The mass of one mole of CaCO₃ is the same as the molar mass of this compound:
. - The mass of one mole of Ca atoms is (numerically) the same as the relative atomic mass of this element:
.
Calculate the mass ratio of Ca in a pure sample of CaCO₃:
.
Let the mass of the sample be 100 g. This sample of CaCO₃ contains 30% Ca by mass. In that 100 grams of this sample, there would be 
of Ca atoms. Assuming that the impurity does not contain any Ca. In other words, all these Ca atoms belong to CaCO₃. Apply the ratio 
:
.
In other words, by these assumptions, 100 grams of this sample would contain 75 grams of CaCO₃. The percentage mass of CaCO₃ in this sample would thus be equal to:
.
<h3>
Answer:</h3>
12 years
<h3>
Explanation:</h3>
We are given;
Half life of hydrogen-3 is 12 years
Initial mass of Hydrogen-3 is 20 grams
Final mass will be 10 g because we are told half of the sample will decay.
To find the time taken for the decay we need to know what half life is;
- Half life is the time taken for a radioactive isotope to decay to half its original amount.
Remaining mass = Original mass × 0.5^n
n = number of half lives
therefore;
10 g = 20 g × 0.5^n
0.5 = 0.5^n
n = log 0.5 ÷ log 0.5
= 1
But, 1 half life is 12 years
Therefore, the time taken is 12 years
<h3><u>Answer and explanation</u>;</h3>
- To balance the charges of ions the number of electrons lost is equal to the number of electrons gained. The overall net charge must be zero.
- The number of ions needed to accomplish this is represented by the subscripts.
- For any given ionic compound, the product of the charge on the ion (or multiatomic ionic group) times the subscript of the ion will give a total charge of zero when all ions are considered.
For examples: NaCl Na = +1 Cl = -1 total is zero
