Samuel Eto'o, wasted down the right in recent weeks, was back in his more favoured central position and he fired an early warning shot wide - but from then on, the first half was nearly all Schalke.
The influential Altintop forced Valdes to divert his 20-yard shot away, before Kuranyi headed wide from a central position six yards out.
Jones was enjoying himself down the right at Eric Abidal's expense and after he lashed a shot inches wide, he sent in a dangerous cross that only just evaded first Asamoah and then, agonisingly, Kuranyi at the far post.
But just before the break Barca, for whom Xavi had earlier seen a shot well saved by Manuel Neuer, hit Schalke with a hammer blow.
Bojan was put in down the right, his cross deflected up off Marcelo Bordon and was headed brilliantly off the line by Mladen Krstajic, only for Toure to side-foot in from six yards as the ball dropped at his feet.
Schalke paid for their profligacy in the Nou Camp
With more space to play in in the second half, Barca finally began to enjoy themselves.
Bojan teed up Thierry Henry to blaze over, before Andres Iniesta forced a stunning save from Neuer, the big keeper getting down wonderfully to his right to tip away a goalbound 22-yard drive.
Just after the hour mark Barca's semi-final first leg hopes suffered a hammer blow when captain Carles Puyol picked up a yellow card that will keep him out of the Nou Camp tie in two weeks' time.
But if the under-pressure Rijkaard thought the result would appease his club's supporters, the crescendo of boos that erupted around the stadium when he took Bojan off told a different story.
The game eventually fizzled out, but Barca know they will need to be much more impressive if they are to overcome Man Utd and reach the final in Moscow in May.
Barcelona coach Frank Rijkaard: "We are looking forward to the Manchester United games a lot, let's prepare for two very exciting games.
"We had to work very hard to beat Schalke - they don't have the individual players, but they work hard as a team and chase you all over the park, so it was difficult, complicated.
"Bojan was great again, for such a young player he is giving so much to the team already and he has won the sympathy of the public which is very important for him."
Barcelona: Valdes, Puyol, Thuram, Zambrotta, Abidal, Iniesta, Toure Yaya (Marquez 81), Xavi, Henry (Gudjohnsen 90), Eto'o, Bojan (Giovanni 72). Subs Not Used: Pinto, Milito, Edmilson, Sylvinho.
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