# Chemistry

Can someone link me videos and sites that can teach me the formula to solve these? Or try to help me understand how to solve these?

1.You have 200g of a radioisotope . If the half-life of this radioisotope is 20 days, how many grams will remain after 40 days?

2.Calculate the molarity of a saline solution prepared by dissolving 19.3g of sodium chloride in 250 mL of water.

3.Calculate the pH of a solution that has [OH-]=1x10^-9

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1. 1. You need no website. If half is gone after 20 days, then after 40 days, half of half is all that remains: 1/4*200=50g
2. Molarity= mass/molmass * 1/volumeinLiters
= 19.3/formalamassNaCl * 1/4
formula mass Na=23+35 check that.
3. pH+pOH=14
pOH=-log(OH)=-log (10^-9)=9
PH=14-9=5

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posted by bobpursley
2. "Samantha,"
You are cheating on your chemistry final. Please review the INCA honor code which you are clearly violating. Sadly, you are only cheating yourself because the goal of school is to become educated. If you are going on to college, your college will expect you to know this information when you get there.

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posted by INCA Teacher

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