Answer:
molar mass = given mass/ no. of moles
Molarity is the number of moles of solute in 1 L of solution
molarity of KBr solution is 0.630 M
this means that there there are 0.630 moles of KBr in 1 L solution
then in 615 mL number of KBr moles are - 0.630 mol/L x 0.615 L = 0.387 mol
mass of KBr is - molar mass x number of moles
KBr molar mass is 119 g/mol x 0.387 mol = 46.1 g
mass of KBr is 46.1 g
When the guard cell is filled with water and it becomes turgid, the outer wall balloons outward, drawing the inner wall with it and causing the stomate to enlarge.
18 g of silicon-32 will be present in 800 years.
A radioactive half-life refers to the amount of time it takes for half of the original isotope to decay and it's given by
![N(t) = N_0 (\frac{1}{2}) ^\frac{t}{t_\frac{1}{2} }](https://tex.z-dn.net/?f=N%28t%29%20%3D%20N_0%20%28%5Cfrac%7B1%7D%7B2%7D%29%20%5E%5Cfrac%7Bt%7D%7Bt_%5Cfrac%7B1%7D%7B2%7D%20%7D)
where,
quantity of the substance remaining
the initial quantity of the substance
time elapsed
the half-life of the substance
From the given information we know:
The initial quantity of silicon-32 is 40 g.
The time elapsed is 800 years.
The half-life of silicone-32 is 710 years.
So, using the calculation above, we can determine how much silicon-32 is left.
![N(t) = 40 (\frac{1}{2}) ^\frac{800}{710} \\N(t) = 40 (\frac{1}{2}) ^\frac{80}{71} \\\\N(t) = 18 g](https://tex.z-dn.net/?f=N%28t%29%20%3D%2040%20%28%5Cfrac%7B1%7D%7B2%7D%29%20%5E%5Cfrac%7B800%7D%7B710%7D%20%5C%5CN%28t%29%20%3D%2040%20%28%5Cfrac%7B1%7D%7B2%7D%29%20%5E%5Cfrac%7B80%7D%7B71%7D%20%5C%5C%5C%5CN%28t%29%20%3D%2018%20g)
Therefore,18 g of silicon-32 will be present in 800 years.
Learn more about half-life here:
brainly.com/question/25750315
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