Young people in Scotland have the most to gain from remaining in the UK and the most to lose from opting for independence, the leader of the pro-union campaign will tell younger voters.
Better Together leader Alistair Darling will use his latest speech to argue that Alex Salmond and his supporters are presenting a negative message to the electorate by "failing to answer basic questions" about the consequences of a yes vote.
He will say that the impact the outcome of the referendum will have on future generations shows why there must be certainty about the decision.
The former chancellor is due to give a speech in Edinburgh to an audience of younger voters.
He will say: "There has been a lot of talk on this campaign about who has the positive and who has the negative message.
"Well, let me tell you this. I can think of little more negative than demanding that Scotland leave a 300-year union that generations of Scots built with our neighbours without any real guarantee about what would come next.
"Take the most fundamental issue at stake in this referendum: Alex Salmond cannot even tell us what money we would carry in our pockets the day after independence.
"I will be voting no. Others will vote yes. Others have yet to make up their minds. But be warned. The biggest of the don't knows is Alex Salmond."
Mr Darling will argue that Mr Salmond is unable to provide answers and guarantees on issues such as currency, mortgages, tax rates and education.
He will add: "That is too negative a message for Scotland to contemplate.
"A vote to separate from the rest of the United Kingdom will be unchangeable. This generation of Scots will have bound the hands of generations of Scots to come. Be in no doubt about the gravity of this decision.
"The question on the ballot paper is not a hypothetical one. The only certainty of an independence vote is that we will leave the United Kingdom, no matter what we lose, no matter what the cost."
Mr Darling is the latest leading figure in the independence debate to argue his case to the public in recent weeks, following speeches from Deputy First Minster Nicola Sturgeon and Scottish Secretary Alistair Carmichael.
Angus Robertson MP, the SNP's Westminster leader, said: "This is desperately poor and panicky stuff from Alistair Darling, who is hastily reacting to the fact that the Yes campaign have the momentum in our referendum year.
"There are no new ideas or messages from the No Campaign - only further evidence that Project Fear is alive and well in 2014.
"Mr Darling sounds rattled, and is out of touch even with his own campaign - the No campaign's expert adviser Professor Gallagher agrees that Scotland will not be part of the euro.
"He is also out of touch with what is happening on the ground - as we have seen in Ayrshire College and Prestwick Academy in recent days, Yes moves into the lead when people hear the positive arguments for an independent Scotland, and they are seeing right through the smears and fears of the No campaign."