Some Basic Conc...

Percentage purity of a sample of gold is $$85\%$$. How many atoms of gold are present in its $$1$$ gram sample? (Atomic mass of gold $$=197$$u).

Volume of $$O_{2}$$ remained after the first combustion?

Calculate the mole percentage of $$CH_{3}OH$$ and $$H_{2}O$$ respectively in $$60$$% (by mass) aqueous solution of $$CH_{3}OH$$.

The vapour pressure of a solution of a non -volatile electrolyte (A) in a solvent (B) is $$95\%$$ of the vapour pressure of the solvent at the same temperature. If $$M_b=0.3 M_A$$, where $$M_B$$and $$M_A$$ are molecular weights of B and A respectively, the weight ratio of the solvent and solute are:

A 5 mL (specific gravity 1.02) of chlorine water is treated with an excess of KI.The liberate iodine required 26 mL of $$ 0.15 \,M-Na_2SO_4$$ solution.Calculate the percentage of $$Cl_2$$ (by weight) the chloride water.Chloride water is a solution of free chlorine in water

$$0.3\ g$$ of an oxalate salt was dissolved in $$100\ mL$$ solution. The solution required $$90\ mL$$ of $$N/20\ KMnO_4$$ for complete oxidation.The % of oxalate ion in salt is: 

How many moles of magnesium phosphate, $$Mg_3(PO_4)_2$$ will contain 0.25 mole of oxygen atoms ? 

A 1.85 g sample of an arsenic-containing pesticide was chemically converted to $$AsO_4^{3-}$$ (atomic mass of As = 74.9) and titrated with $$Pb^{2+}$$ to form $$Pb_3(AsO_4)_2$$. If 20 mL of 0.1 M $$PB^{2+}$$ is required to reach the equivalence point, the mass percentages of arsenic in the pesticide sample is closest to

A $$1.85\ g$$ sample of an arsenic-containing pesticide was chemically converted to $$AsO_{4}^{3-}$$ (atomic mass of $$As = 74.9)$$ and titrated with $$Pb^{2+}$$ to form $$Pb_{3}(AsO_{4})_{2}$$. If $$20\ mL$$ of $$0.1\ M\ Pb^{2+}$$ is required to reach the equivalence point, the mass percentage of arsenic in the pesticide sample is closest to:

4.0 g of a mixture of $$NaCl$$ and an unknown metal iodide $$MI_{2}$$ was dissolved in a water to form its aqueous solution. To this aqueous solution, The aqueous solution $$AgNO_{3}$$ was added gradually so that silver halides are precipitated. The precipitates were weighed at regular interval and the given curve for the mass of precipitate versus volume of $$AgNO_{3}$$ added was obtained. With the knowledge of the fact that halides are precipitated successively i.e. when one halide is precipitating , the other halide remains in the solution, answer the following questions:
(Molar mass of $$Ag = 108,\ I = 127,\ Na = 23$$).
Points $$P$$ and $$Q$$ are: $$P(20, 4.8),\ Q(37, 7.25)$$
What is the approximate mass percentage of $$MI_{2}$$?