Molality is defined as the number of moles of solute in 1 kg of solvent.
molality of solution to be prepared is 0.50 molal
this means that in 1000 g of water there should be 0.50 mol of NaCl
if 1000 g of water should contain - 0.50 mol
then 750.0 g of water requires - 0.50 mol/kg x 0.750 kg = 0.375 mol
mass of NaCl in 0.375 mol - 58.5 g/mol x 0.375 mol = 21.9 g
therefore a mass of 21.9 g of NaCl is required
Answer:
% oxygen = 47.1 %
% aluminium = 52.9 %
Explanation:
Step 1: Data given
Mass of aluminium = 2.70 grams
Mass of aluminium oxide = 5.10 grams
Step 2: The balanced equation
4Al + 3O2 →2Al2O3
Step 3: Calculate mass of oxygen
The law of conservation of mass states that in a chemical reaction, the total mass of reactants is equal to the total mass of products.
Mass oxygen + mass aluminium = mass aluminium oxide
Mass oxygen + 2.70 grams = 5.10 grams
Mass oxygen = 5.10 grams - 2.70 grams
Mass oxygen = 2.40 grams
Step 4: Calculate percent composition
% oxygen = (mass oxygen / mass aluminium oxide) * 100 %
% oxygen = (2.40 grams / 5.10 grams ) * 100 %
% oxygen = 47.1 %
% aluminium = (mass aluminium / mass aluminium oxide)
% aluminium = (2.70 grams / 5.10 grams ) * 100 %
% aluminium = 52.9 %
47.1 % + 52.9 % = 100 %
Answer:
1.2 ( two significant digits)
Explanation:
5.4 - 4.21 answer should only have the the number of significant digits as the number in the equation with the least number of significant digits... in this case 5.4 is only two significant digits....so the answer should only have two significant digits
5.4 - 4.21 = 1.19 round to two digits = 1.2
<span>According to modern atomic theory, electrons can't move from one energy
level to another. It is not that it cannot really move but electrons tend to stay at a level with the lowest energy possible. Hope this answers the question. Have a nice day.</span>