Why my percentage yield is much less than 100%?

what couze that ?

Determine the percent ionic charcter of the following bonds, based on the electronegativity differences: Show your work.

a. NaCl

b. FeCl2

c. CuCl

d. AlCl3

e. CCl4

Calculate the mass of sodium acetate trihydrate required to make 100. mL of a 0.100 M solution.

Sulfuric acid dissolves aluminum metal according to the following reaction: 2Al(s)+3H2SO4(aq)?Al2(SO4)3(aq)+3H2(g) Suppose you wanted to dissolve an aluminum block with a mass of 14.7g .

Part A

What minimum mass of H2SO4 would you need?

Express your answer in grams.

Part B

What mass of H2 gas would be produced by the complete reaction of the aluminum block?

Express your answer in grams.

Why is a Diels-Alder reaction favored at lower temperature? Please give a clear and specific answer.

calculate the concentrations of H+, HCO- and CO3^2- in a 0.025 M H2CO3 solution

5.         From the information below, determine the mass of substance C that is formed if 45.0 g of substance A reacts with 23.0 g of substance B, assuming that the reaction between A and B goes to completion.

A. Substance A is a solid that consists of a Group 13 (3A) metal (boron is not a metal!) and carbon; the m% C in substance A is 57.2%. It reacts with substance B to form substances C and D. 4.0 x 10¹⁶ formula units of substance A weighs 8.371 micrograms.

B. 47.9 g of substance B contains 5.36 g H and 42.5 g O.

C.   When 10.0 g of substance C is burned in excess oxygen, 33.8 g of CO₂and 6.92 g of H₂O are produced. The molar mass of substance C is M_C = ~26 g/mol.

D. Substance D is the hydroxide of the metal in substance A.

Discuss how a distillation works; also include the difference between a simple and a fractional distillation. Why is fractional distillation used in preparation of cyclohexene?

Consider the titration of 25.0 mL of 0.0200 M MnSO4 with 0.0100 M EDTA in a solution buffered to pH=6.00. Calculate pMn2+ at the following volumes added EDTA, and use your data to sketch a titration curve for they hypothetical sample: 0, 20.0, 40.0, 49.0, 49.9, 50.0, 50.1, 55.0, and 66.0 mL.

Find information on:

1. epinephrine

2. cholic acid

3. ibuprofen (both enantiomers)

4. naproxen

To get full credit (4 pts) you must: 1. Give molecular formula and structure

2. Identify each carbon’s hybridization

3. Identify one stereocenter and it’s configuration

4. Identify the molecule’s importance and/or application

A 6.79-L cylinder contains 2.00 mol of gas A and 3.96 mol of gas B, at a temperature of 31.5 °C. Calculate the partial pressure of each gas in the cylinder. Assume ideal gas behavior.

A solution of .05 M glutamic acid is at its isoelectric pH. Calculate:
i) the approximate concentration of its major isoelectric form
ii) the approximate concentration of the completely protonated form
iii) How may forms are present in solution at even miniscule concentrations?

What methods and calculations are used in order to obtain the pH of a system with changing dynamics? Please include a mathematical example to accompany each case and solve at pH 3, 7 and 10.

a) Addition of weak base to weak acid

b) Addition of strong base to weak acid

c) Addition of weak base to strong acid

d) Addition of strong base to strong acid

Which of the following samples contains the largest total number of atoms? Please show work

a) 0.10 moles of P4O10

b) 0.20 moles of P4O6

c) 0.30 moles of N2O5

d) 0.40 moles of N2O4

e) 0.50 moles of BiF3

After running a base catalyzed hydrolysis of nicotinitrile with anion-exchange resins, how can I determine if I ended up with niacin or nicotinamide, without melting point ranges, or NMR?