When a substance undergoes a physical change no new substance is formed.
Answer:
According to mass and volume, block density is 2 g/ml
Explanation:
Density is a measure, usually used in physics and chemistry, that relates the mass and volume of a solid or compound.
In general terms, the density is directly proportional to the mass, and inversely proportional to the volume, so increasing the mass will also increase the density.
The formula used to calculate the density is
ρ = 
Therefore, according to the mass and density of the block
ρ = 
= 2g/ml
Being the density of the block equal to 2 g/ml.
<em>The other options are not possible, because the values given do not correspond to the result of the equation.</em>
Answer:
0.056moles HF and 0.70M
Explanation:
When a strong acid is added to a buffer, the acid reacts with the conjugate base.
In the system, NaF and HF, weak acid is HF and conjugate base is NaF. The reaction of NaF with HCl (Strong acid) is:
NaF + HCl → HF + NaCl
Initial moles of NaF and HF in 60.0mL of solution are:
NaF:
0.0600L × (0.80mol / L)= 0.048 moles NaF
HF:
0.0600L × (0.80mol / L)= 0.048 moles HF
Then, the added moles of HCl are:
0.0200L × (0.40mol / L) = 0.008 moles HCl.
Thus, after the reaction, moles of HF produced are 0.008 moles + the initial 0.048moles of HF, moles of HF are:
<em>0.056moles HF</em>
<em></em>
In 20.0mL + 60.0mL = 80.0mL = 0.0800L, molarity of HF is:
0.056mol HF / 0.0800L = <em>0.70M</em>
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