CARBON is the element that must be present in an organic compound.
Answer:
1) 0.0625 g.
2) 0.0125 g.
Explanation:
<em>1) A solution of NaOH has a concentration of 25.00% by mass. What mass of NaOH is present in 0.250 g of this solution?</em>
mass% of NaOH = [(mass of NaOH)/(mass of solution)] x 100.
mass% of NaOH = 25.0%, mass of NaOH = ??? g, mass of solution = 0.250 g.
∴ mass of NaOH = (mass% of NaOH)(mass of solution)/100 = (25.0%)(0.250 g)/100 = 0.0625 g.
<em>2) What mass of NaOH must be added to the solution to increase the concentration to 30.00% by mass?</em>
We can use the relation:
mass% of NaOH = [(mass of NaOH)/(mass of solution)] x 100.
mass% of NaOH = 30.0%, mass of NaOH = ??? g, mass of solution = 0.250 g.
∴ mass of NaOH = (mass% of NaOH)(mass of solution)/100 = (30.0%)(0.250 g)/100 = 0.075 g.
∴ The mass of NaOH should be added = 0.075 - 0.0625 = 0.0125 g.
Answer: -
1 mol
Explanation: -
Number of moles of Sulphur S = 7
Number of moles of O2 = 9
The balanced chemical equation for the reaction is
2S (s)+3 O2 (g)→2SO3(g)
From the above reaction we can see that
3 mol of O2 react with 2 mol of S
9 mol of O2 will react with

= 6 mol of S
Unreacted S = 7 - = 1 mol.
If a reaction vessel initially contains 7 mol S and 9 mol O2
1 mole of s will be in the reaction vessel once the reactants have reacted as much as possible
The question is incomplete,the complete question :
Calculate the molality of a 10.0% (by mass) aqueous solution of hydrochloric acid:
a) 0.274 m
b) 2.74 m
c) 3.05 m
d) 4.33 m
e) the density of the solution is needed to solve the problem
Answer:
The molality of a 10.0% (by mass) aqueous solution of hydrochloric acid is 3.05 mol/kg.
Explanation:
10.0% (by mass) aqueous solution of hydrochloric acid.
10 grams of HCl is present in 100 g of solution.
Mass of HCl = 10 g
Mass of solution = 100 g
Mass of solution = Mass of solute + Mass of water
Mass of water = 100 g - 10 g = 90 g
Moles of HCl = 
Mass of water in kilograms = 0.090 kg
Molality = 
The molality of a 10.0% (by mass) aqueous solution of hydrochloric acid is 3.05 mol/kg.
Answer: Paramagnetism is most easily observed in the salts of some of the first row transition metals (manganese through nickel). The se metal ions have unpaired electrons in degenerate d orbitals as predicted by Hund's rule and thus exhibit paramagnetism.
Explanation: METALS ARE ELECTRONS
AND PARAMAGNETIC OBSERVES SALT FORST ROWS ONLY