4. pH of the blood is 7.4. The organism uses bicarbonate buffer to maintain the narrowly defined value. Calculate how much of NaHCO3 should be added to 1 L of solution at a concentration of
0.250 mol/L of H2CO3 (PKA = 6.35) to maintaining of blood pH.
[2.81 mol]
Someone know how to do this exercise?

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).

yes

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as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2