Phenolphthalein is not a good indicator to use for a titration for a solution that has a ph of 6.0 at the equivalence point because the color change of the solution at this pH level is not sharp. It changes the color of the solution to pink starting from pH 8.3 to 10. A pH level lower than 8.3 would only show a colorless solution. Thus, you would not be able to distinguish whether the solution has reached its equivalence point at pH 6.0. It is best to use this indicator for a system that is using a strong base titrated with a weak acid.
Answer: The activation energy is 10 kJ and the reaction is exothermic.
Explanation: Exothermic reactions are those in which heat is released and thus the energy of products is less than the energy of reactants.
Endothermic reactions are those in which heat is absorbed and thus the energy of products is more than the energy of reactants.
Activation energy is the extra amount of energy required by the reactants to cross the energy barrier to convert to products.
Given : Energy of reactants = 40kJ
Energy of activation: (50-40)=10 kJ
Energy of products = 50 kJ
Energy of products = 15 kJ
Thus Energy of products (15kJ) < Energy of reactants(40kJ), the reaction is exothermic as energy has been lost to surroundings in the form of heat.
Ethene react with oxygen at a 
molar ratio:
Convert the quantity of each reactant supplied to number of moles of particles:
The question stated not whether both reactants were used up in this process. Thus start by testing the assumption that e.g., ethene was used up while some oxygen gas were left unreacted (ethene as the <em>limiting </em>reagent.) Under this assumption, the relative availability of the two species, 
and 
(as seen in the balanced chemical equation) shall satisfy the relationship
In other words,
Evaluating the expression 
with data given in the question yields approximately 
, which does satisfy the relationship. Hence the assumption holds and ethene is the limiting reactant.
The quantity of a reactant produced in a chemical reaction is related to its stoichiometric (of relating to proportions) relationship with the limiting reactant (or any of the reactants in case of more than one limiting reactant.) For this scenario, given the molar ratio 
,
From the calcuation, the percent ionic character of the bond is 70%
<h3>What is percent ionic character?</h3>
The term percent ionic character has to do with the degree of ionic bonding that is contained in a compound. It can be estimated from the electronegativity of each element.
We can use the formula; 100(1 - e^(-ΔEN² / 4))
EN = χB − χA * 100/1
EN = 3.5 - 1.5 = 1
100(1 - e^(-1)^2/4)
= 70%
Learn more about percent ionic character:brainly.com/question/7034446
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Calcium carbonate is CaCO3.
So there is calcium, symbol is Ca and an atomic number of 20.
Carbon: symbol is C and an atomic number of 6.
Oxygen: symbol is O and an atomic number of 8.
In one molecule of CaCO3, there is one atom of Ca, one atom of C, and three atoms of O as shown by the subscript next to O in the formula. There are no other subscripts to indicate more than one atom of the other elements, so there is only one atom of the other two elements
