Use the Heat formula for both problems.
q=m*c*∆t
Where
q= heat in Joules
m= mass in grams
c= specific heat which is a constant 4.18
∆t= change in temperature
silver tarnishes is a chemical change
Answer:
Cr (HSO4)3
Explanation:
its molecular weight is 343.20 g/mol
its molecular formula can also be written as CrH3O12S3
molar mass of Cr (HSO4)3 can be calculated by following method;
atomic mass of Cr = 51.9961 u
atomic mass of H = 1 u
atomic mass of S = 32.065 u
atomic mass of O = 16 u
molar mass of Cr(HSO4)3 = 51.9961+ 1.00784×3 + 32.065×3 + 15.999×12
molar mass of Cr(HSO4)3 =51.9961+3.02352+96.195+ 191.988
molar mass of Cr(HSO4)3 = 343.20 g/mol
The number of mole of HCl needed for the solution is 1.035×10¯³ mole
<h3>How to determine the pKa</h3>
We'll begin by calculating the pKa of the solution. This can be obtained as follow:
- Equilibrium constant (Ka) = 2.3×10¯⁵
- pKa =?
pKa = –Log Ka
pKa = –Log 2.3×10¯⁵
pKa = 4.64
<h3>How to determine the molarity of HCl </h3>
- pKa = 4.64
- pH = 6.5
- Molarity of salt [NaZ] = 0.5 M
- Molarity of HCl [HCl] =?
pH = pKa + Log[salt]/[acid]
6.5 = 4.64 + Log[0.5]/[HCl]
Collect like terms
6.5 – 4.64 = Log[0.5]/[HCl]
1.86 = Log[0.5]/[HCl]
Take the anti-log
0.5 / [HCl] = anti-log 1.86
0.5 / [HCl] = 72.44
Cross multiply
0.5 = [HCl] × 72.44
Divide both side by 72.44
[HCl] = 0.5 / 72.4
[HCl] = 0.0069 M
<h3>How to determine the mole of HCl </h3>
- Molarity of HCl = 0.0069 M
- Volume = 150 mL = 150 / 1000 = 0.15 L
Mole = Molarity x Volume
Mole of HCl = 0.0069 × 0.15
Mole of HCl = 1.035×10¯³ mole
<h3>Complete question</h3>
How many moles of HCl need to be added to 150.0 mL of 0.50 M NaZ to have a solution with a pH of 6.50? (Ka of HZ is 2.3 x 10 -5 .) Assume negligible volume of the HCl
Learn more about pH of buffer:
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