Chem Calculations

Question

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1.If the formula of a hydrated compound is MgSO4‧xH2O and the

percentage by mass of water of crystallization is 51.22,what is the value of

x??

A.7

B.6

C.5

D.4

2.Magnesiumhydroxide is the active ingredient of an antacid. A 6g tablet of

this antacid is dissolved in water and is made up to 250cm3. 25cm3 of the

solution is titrated against 1.45M HCL. 7cm3 of the acid is required for

complete neutralization.What is the percentage by mass of magnesium

hydroxide in a tablet of the antacid?

A.43.54%

B.49.06%

C.87.08%

D.98.12%

Answer 1

最愛解答

1)The total molecular mass= 24.3+32.1+16x4+18x=120.4+18x

% of water

18x/(120.4+18x) x100%=51.22

x=7.03 ~=7

2) H+ +OH- ---> H2O

In 25cm^3

number of mole of OH-= 7/1000*1.45=0.01015

total number of mole Mg(OH)2 = 0.01015x10/2=0.05075

total mass of Mg(OH)2 = 2.958g

% by mass of Mg(OH)2= 2.958/6X100% =49.3%

第一題, 當佢比例數咁做就得

第2題, 因為1mole Mg(OH)2 可以出2mole OH- ion

所以titration 既HCl 既mole 要除2 先係number of mole of Mg(OH)2 既MOLE

之後就係普通既mole數計法

如果錯左請通知