Answer:
The most effective buffer at pH 9.25 will be a mixture of 1.0 M NH3 and 1.0 M NH4Cl
Explanation:
Step 1: Data given
pH of a buffer = pKa + log ([A-]/[Ha])
a mixture of 1.0 M HC2H3O2 and 1.0 M NaC2H3O2 (Ka for acetic acid = 1.8 x 10-5)
pH = -log( 1.8 * 10^-5) + log (1/1)
pH = -log( 1.8 * 10^-5)
pH = 4.74
a mixture of 1.0 M NaCN and 1.0 M KCN (Ka for HCN = 4.9 x 10-10)
pH = -log( 4.9 * 10^-10) + log (1/1)
pH = -log( 1.8 * 10^-5)
pH = 9.30
a mixture of 1.0 M HCl and 1.0 M NaCl
The solution made from NaCl and HCl will NOT act as a buffer.
HCl is a strong acid while NaCl is salt of strong acid and strong base which do not from buffer solutions hence due to HCl PH is less than 7.
a mixture of 1.0 M NH3 and 1.0 M NH4Cl (Kb for ammonia = 1.76 x 10^-5)
Ka * Kb = 1*10^-14
Ka = 10^-14 / 1.76*10^-5
Ka = 5.68*10^-10
pH = -log( 5.68*10^-10) + log (1/1)
pH = -log( 5.68*10^-10)
pH = 9.25
The most effective buffer at pH 9.25 will be a mixture of 1.0 M NH3 and 1.0 M NH4Cl
240 g NaOH
<em>Step 1</em>. Calculate the moles of NaOH
Moles of NaOH = 0.750 L solution × (8 mol NaOH/1 L solution) = 6 mol NaOH
Step 2. Calculate the mass of NaOH
Mass of NaOH = 6 mol NaOH × (40 g NaOH/1 mol NaOH) = 240 g NaOH
Given parameters;
Mass of gold colored metal beads = 425g
Volume of water displaced by beads = 48.0cm³
Unknown;
Identity of the metal = ?
Given densities;
Gold: 19.3 g/mL
Copper: 8.86 g/mL
Bronze: 9.87 g/mL
Density is an intensive property of any substance. This implies that we can use the density of any substance to identify it.
Density can be defined as the mass per unit volume of a substance. Every substance has a unique mass per volume.
Mathematically;
Density = 
where mass is in kg or g
volume is in m³ or cm³
To find the density, we must know the mass and volume.
In this problem, the volume of the gold metal beads is the same as the volume of water displaced. This is a way to measure volume of solids.
Since the volume is given in cm³, and we are comparing with choices that have units in g/mL, we simply convert the volume in cm³ to mL
1cm³ = 1mL³
So therefore, volume of gold colored metal is 48mL
Now input the parameters given and solve for the density;
Density =
= 8.85g/mL
From the given densities, we clearly see that copper is the metal since they both of similar densities.