Answer:
1. 6.005 g
2. 22.9 mL
3. Until the mixtures becomes homogeneous.
Explanation:
A buffer is a solution where a weak acid is in equilibrium with its conjugate base (its anion) or a weak base is in equilibrium with its conjugate base (its cation). The buffer remains the pH almost unaltered because it shifts the equilibrium if an acid or base is added.
1. The pH of a buffer can be calculated by the Henderson-Hasselbalch equation:
pH = pKa + log[A⁻]/[HA]
Where [A⁻] is the concentration of the conjugate base (the anion) of the acid, and HA is the acid concentration.
5.10 = 4.76 + log[A⁻]/[HA]
log[A⁻]/[HA] = 5.10 - 4.76
log[A⁻]/[HA] = 0.34
[A⁻]/[HA] =
[A⁻]/[HA] = 2.1878
Because the volume is the same, we can replace the concentration by the number of moles (n):
nA⁻/nHA = 2.1878
nA⁻ = 2.1878*nHA
The total number of moles of the substances in the buffer is: 0.200 mol/L * 0.5 L = 0.1 mol
nA⁻ + nHA = 0.1
2.1878*nHA + n HA = 0.1
3.1878nHA = 0.1
nHA = 0.0314 mol
nA⁻ = 0.0686 mol
The total number of moles of acetic acid needed is 0.1 mol (both substances may be from it):
m = MW*mol
m = 60.05*0.1 = 6.005 g
2. NaOH must react with acetic acid to form the anion, so for a 1:1 reaction, it will be needed 0.0686 mol of NaOH:
V = mol/concentration
V = 0.0686/3
V = 0.0229 L = 22.9 mL
3. The buffer must be a homogeneous solution, it means that it can't be noticed phases in the buffer, so the flask must be inverted until all the buffer is diluted in water, and it will be noticed when the solution becomes homogenous.
Answer:
A physical change is a change from one state of matter to another; a chemical change results in a new substance formed.
<u><em>Physical properties:</em></u>
Physical properties are those which have same composition. In other words, composition does not change, only state may be change like solid to liquid, liquid to gas, solid to liquid etc.
<u><em>Example. </em></u>
Water when freezes into ice, it is physical change, just state is change.
<em><u>Chemical properties:</u></em>
The chemical properties depend upon composition.
<u>Example:</u>
Formation of precipitates is an example of chemical change.
NO₃⁻ is the polyatomic ion in this case.
Answer:
d- Scientists have to follow government rules made to protect people.
Explanation:
Scientific research fosters our understanding of the world around us. It helps people to learn to promote critical thought and problem-solving. Although there may not be an immediate practical use of the research, in the long term the study could benefit humanity. Scientific research is the product of creative ideas and collaborative communication that the proper role of government is often restricted to funding the research. The role of the government is to perform its reasonable and valid duties of defending human rights and enhancing the independence of the human.
Answer:
Electron geometry- Tetrahedral
Molecular geometry- Bent
Bond angle- <<109.5°
Explanation:
According to the Valence Shell Electron Pair Repulsion (VSEPR) Theory, the shape of a molecule depends on the number of electron pairs present bon the central atom of the molecule. The electron pairs orient themselves as far apart in space as possible to minimize repulsion between electron pairs.
However, the repulsion between all electron pairs is not the same. Lone pairs cause more repulsion around the central atom than bond pairs. Hence lone pairs tend to distort the molecular structure away from that predicted on the basis of Valence Shell Electron Pair Repulsion Theory.
Considering XY2Z2, there are four electron domains, two bond pairs with bonding groups at 180° apart and two lone pairs. Based on VSEPR theory, a tetrahedral shape is expected with a bond angle of about 109°.
The presence of two lone pairs distorts the observed molecular geometry to a bent shape with bond angle <<109°, hence the answer above.