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A mixture contains Na2CO3 and NaHCO3 and wt. of mixture is 10gm. Mixture on heating liberates 56ml of CO2 at S.T.P, wt of Na2CO3 in mixture is

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Explanation

Only NaHCOevolve CO2 gas. Na2CO3 does not evolve CO2 gas even on red heating.

So, the only reaction happening is: 

2NaHCO3 -> Na2CO3 + CO2 + H2O

Weight: 

2(23+1+12+16*3) -> (2*23+12+16*3) + (12+16*2) +  (1*2+16)
                               
    168g                 ->         102g          +       44g      +    18g

Also, COmass as per 56ml volume obtained at STP = 56/(22.4 * 1000) * (44) = 0.11g

So, NaHCOweight = 0.11/44*168 = 0.42g (using ratio of weights from equation)

Therefore, original Na2CO3 weight in the original mixture = 10 - 0.42 = 9.58g

How many moles of KMnO4 are needed a mixture of 1 mole of each FeSO4 & FeC2O4 in acidic medium

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Explanation

Equivalents of KMnO4 = equivalent of FeSO4 + equivalent of FeC2O4

x × 5=1 × 1 + 1 × 3

x = 45 mole

The percentage of copper in a copper(II) salt can be determined by using a thiosulphate titration. 0.305 gm of a copper(II) salt was dissolved in water and added to, an excess of potassium iodide solution liberating iodine according to the following equation 2Cu2 (aq) + 4I (aq) 2CuI(s) + I2(aq) The iodine liberated required 24.5cm3 of a 0.100 mole dm-3 solution of sodium thiosulphate 2S2O32- (aq) + I2(aq) 2I (aq) + S4O62- (aq) the percentage of copper, by mass in the copper(ll) salt is. [Atomic mass of copper = 63.5]

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Explanation

From given reactions

mmoles of hypo = mmoles of iodine × 2

= mmoles of Cu2+ ions

= 24.5 × 0.1 mmoles

So mass of copper = 24.5 × 0.1 × 10–3 × 63.5 gm

So % of copper = 24.5×0.1×103×63.50.305×100%51.0%

Oxygen contains 90% O16 and 10% O18. Its atomic mass is [KCET 1998]

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Explanation

Average atomic mass of oxygen =90  ×  16  +  10  ×  18100=16.20  

KClO3 on heating decomposes to KCl and O2. The volume of O2 at STP liberated by 0.1 mole KClO3 is

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Explanation

On heating KClO3 dissociates as:

2KClO3  Δ2KCl+3O2

2 moles 3 × 22.4 L at STP

2 moles of KClO3 on heating produces = 67. 2 L of O2 at STP

0.1 mole of KClO3on heating produces = 67.22  ×  0.1L = 3.36 L of O2 at STP

At S.T.P. the density of CCl4 vapour in g/L will be nearest to [CBSE PMT 1988]

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Explanation

1 mole of CCl4 vapour = 12 + 4 × 35.5 = 154 gm = 22.4 L at S.T.P.

∴ Density =15422.4gmL1=6.875gmL1  

1 c.c of N2O at NTP contains : [CBSE PMT 1988]

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Explanation

22400 c.c. = 6.02 × 1023 molecules

1 c.c. of N2O=6.02×102322400 molecules

=3×6.02×102322400 atoms (Since N2O has three atoms)

=6.02×102322400×22 electron (Because number of electrons in N2O are 22) 

The mass of carbon present in 0.5 mole of K4[Fe(CN)6] is

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Explanation

1 mole of K4[Fe(CN)6] =6 gm atoms of carbon

0.5 mole of K4[Fe(CN)6] = 3 gm atoms of carbon

= 3 × 12 = 36 g

The number of moles of BaCO3 which contains 1.5 moles of oxygen atoms is [EAMCET 1991]

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Explanation

∵ 1 mole of BaCO3contains 3 moles of oxygen atoms.

12 mole (0.5) of BaCO3 contains 1.5 moles of oxygen atoms.

The oxide of a metal contains 40% by mass of oxygen. The percentage of chlorine in the chloride of the metal is [BIT Ranchi 1997]

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Explanation

% of oxygen = 8m+8  ×  100  =  40 or, 40(m+8)=800 or, m + 8 = 20or, m = 12

∴ % of chlorine = 35.5m+35.5×100 = 35.512+35.5×100 = 74.7(Where m is the atomic mass of metal) 

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