Find the formula of substances of this composition: a) N-35%; O-60%; H-5%;
Find the formula of substances of this composition: a) N-35%; O-60%; H-5%; b) Mg-9.9%; S-13%; O-71.4%; H-5.7% K-39.67% Mn-27.87% O-32.46%
A) Given: N-35%; O-60%; H-5%
Decision:
Let us take as the initial that we have 100 g in-va, then,
m (N) = 100 * 0.35 = 35g
m (O) = 100 * 0.6 = 60g
m (H) = 100 * 0.05 = 5g
n = m / M
n (N) = 35g / (14g / mol) = 2.5 mol
n (O) = 60g / (16 g / mol) = 3.75 mol
n (H) = 5
We are looking for a ratio.
n (N): n (O): n (H) = 2.5: 3.8: 5 = 1: 2: 2. The formula will be NO2H2. Now let’s transform: H2NO2
Answer: H2NO2.
B) Given: Mg-9.9%; S-13%; O-71.4%; H-5.7%
Decision:
m (Mg) = 100 * 0.099 = 9.9 g
m (S) = 100 * 0.13 = 13g
m (O) = 71g
m (H) = 5.7g
n (Mg) = 9.9 g / (24 g / mol) = 0.4 mol
n (S) = 13g / (32 g / mol) = 0.4 mol
n (O) = (71.4 g) / (16 g / mol) = 4.46 mol
n (H) = (5.7 g) / (1 g / mol) = 5.7 mol
n (Mg): n (S): n (O): n (H) = 0.4: 0.4: 4.46: 5.7 = 1: 1: 11: 14
Formula – MgSO11H14
We transform the formula: MgSO4 * 7H2O
Answer: MgSO4 * 7H2O.
B) Given: K-39.67% Mn-27.87% O-32.46%
Decision:
m (K) = 39.67 g
m (Mn) = 27.87 g
m (O) = 32.46 g
n (K) = 39.67g / (39g / mol) = 1 mol
n (Mn) = 27.87g / (55g / mol) = 0.5 mol
n (O) = 32.46g / (16g / mol) = 2mol
n (K): n (Mn): n (O) = 1: 0.5: 2 = 2: 1: 4
formula – K2MnO4. Doesn’t need transformation.
Answer: K2MnO4
